The present invention relates to nacreous pigments having a yellow powder color (e.g., generally wavelengths of 530-590 nm) and improved light-fastness and which are based on mica flakes which are coated with titanium dioxide and to which an additional coloring protective layer has been applied.
It is known, not only from German Pat. No. 1,467,468 but also from German Offenlegungsschrift No. 2,852,585, that an additional thin chromium hydroxide layer on mica platelets coated with titanium dioxide effects an improvement in the stability to light of the base pigments. While German Pat. No. 1,467,468 describes the beneficial influence of a chromium hydroxide coating on mica coated with TiO.sub.2 in anatase form, German Offenlegungsschrift No. 2,852,585 describes the analogous influence on mica coated with TiO.sub.2 in rutile form. The two patents aim at obtaining uncolored TiO.sub.2 /mica pigments.
However, even these improved pigments are not fully satisfactory, since there has still been a demand for pigments having improved light-fastness. There is, in particular, a demand for light-fast nacreous pigments having a deep golden luster (pearlescence) and, in addition but also in general, for pigments having a yellow powder color and optional interference colors.